1. Field of Invention
The present invention relates generally to a shelf, and more particularly to a shelf for storing electronic plug-in units.
2. Description of the Related Art
The modern trend in design of electronic devices is to configure the device as plug-in modules capable of being racked in a shelf. Such plug-in modules are often provided with a multipoint connector that is plugged into a corresponding connecting strip on the back panel (i.e. the backplane) of the shelf.
In order to standardize shelf management implementation, the AMC (Advanced Mezzanine Card) Standard developed by the PICMG (PCI Industrial Computer Manufacturers Group) defines the specifications for plug-in modules and the shelves. The plug-in devices that conform to these specifications are relatively small and are provided with a front panel that is mounted on the circuit board. Such plug-in devices are fit for a special shelf, for which the size and shape are defined in the PICMG Specifications MicroTCA. A shelf of this type includes an upper and a lower support plate spaced apart by two side walls. Guide rails with guide grooves for the circuit boards are arranged on the support plates. These guide rails can be integrated into the support plates by reshaping the material of the support plates, or they can be installed as separate units make of metal or plastic on the support plates.
One special feature of a MicroTCA shelf for AMC modules is that there are no barriers to stop the front panels of the plug-in modules because the backplane of the shelf serves as the stoppage point for the back edge of the circuit boards. Instead, the AMC Standard specifies a locking mechanism, for which a locking projections on the support plate is engaged by a catch on the plug-in module. The AMC standard specifies extremely small dimensions for the locking projection.
In conventional metal support plates for MicroTCA shelves include locking projections that form upward-pointing bulges in the sheet metal plate, which has the advantage of making them extremely stable. An important disadvantage of the conventional support plates, however, is that the position of the locking projections is not flexible, meaning that either separate locking projections must be provided on the support plate for different guide rail positions, or the guide rails can be mounted only at a few predetermined positions on the support plate. Therefore, configurations with plug-in units of different widths are not possible for all practical purposes.
The aforementioned method of forming the locking projections onto the freely positioned guide rails cannot be used where the guide rails are made of plastic material because the plastic material are not nearly strong enough to withstand the mechanical stress exerted when locking a plug-in module in place. The individual arrangement of the locking projections on the support plate is thus required for a shelf that can be equipped flexibly and can accommodate plug-in units with front panels of different widths.